This document provides information on the biology of laboratory mice and rats. It begins with an introduction and course syllabus on the use of animals in research and their anatomy, physiology, reproduction and care. Key points include mice and rats being the most commonly used laboratory animals, with strains like C57BL/6 mice and Sprague-Dawley rats widely used. Their sensory abilities like vision, hearing, smell and touch are described. Details are provided on their reproductive cycles, breeding, strains and suppliers. Factors influencing breeding performance are also discussed.
2. COURSE SYLLABUS:
⚫Introduction and use of animals for different
areas of research
⚫History of animal experimentation
⚫Biology of laboratoryanimals (comparative
anatomy, physiology)
⚫Reproductionand breeding care and housing
4. CLASSIFICATION OF COMMONLY
USED LABORATORYANIMALS
Kingdom Animalia
Phylum Chordata
Class Mammalia
Order Rodents
Family Muridae
Genus Rattus Mus
Species 64 species 34 known species
5. HISTORY OFANIMAL
EXPERIMENTATION
LadyAbbie Lathrop with a mouse Dr. HalseyJ. Bagg , developerof
BALB/c
Mouse - House mouse (Mus musculus) – usage 1600’s, -
increased during 1800’s with increasingresearch activity
9. 1. Rat 2. Mouse 3. Rat 4. Mouse
5. Mouse 6. Rat 7. Rat 8. Rat
9. Mouse 10. Mouse 11. Rat 12. Mouse
10. Feature Rat Mouse
Head
short,stubby
,broad,large
relative to body
small, triangular
,small
relative to body
Muzzle
large and blunt with wide
muzzle
narrow with sharp muzzle
Ears
ears are small relative to
the head
ears are large relative to
the head
Tail thick thin
Tail/body ratio T
ail shorter than body
T
ail same length/longer
than body
Feet
Large relative to body
,
especially the hind feet
Small relative to body
Weight
around 100 grams at 6
weeks,200 grams at 8
weeks
30-50 grams
13. SUPPLIERS AND REPOSITORIES
Most widely used
✓Mouse strains are C57BL/6 mice, BALB/c mice,
✓Rat strain-Sprague-Dawley rats and Wistar rats.
(Labome Survey, 2018)
SUPPLIERS OF ANIMALS
The Jackson Laboratory, Charles River Laboratories,
Taconic Farms and Harlan Laboratories
WEB RESOURCES : Where to look for a specific mouse
strain?
➢INTERNATIONAL MOUSE STRAIN RESOURCE (IMSR)
A collaboration of many international mouse repositories,
containing information for 51,503 strains and 217,063 cell lines
15. MOUSE - SALIENT BIOLOGICAL FEATURES
⚫ Most commonly used among rodents
➢ Small & easy to handle
➢ Short life span & gestation period
➢ Require small housing space and economic
to maintain
⚫ No sweat glands ….only in foot pad??
⚫ Use tail & brown fat - thermoregulation
⚫ Incisor teeth - open rooted (hypsodontic)
grow continuously throughout life
⚫ 5 pairs of mammary gland
16. RAT- SALIENT BIOLOGICALFEATURES
⚫ Dental formula: 2 (incisors 1/1 canines %
premolars % molars 3/3) = 16.
⚫ Incisors grow continuously throughout life,
⚫ No tonsil or gallbladder or receptors for water
and taste
⚫ Diffuse pancreas - diabetic model??
⚫ Coprophagic - not ideal - nutritional studies.
⚫ Uteri - bicornuate duplex
⚫ Do not vomit - strong cardioio-esophageal
sphincter & lack vomiting centre
21. Vision
⚫ Dichromatic vision
⚫ Nocturnal - retina
dominated by rods (dim
light vision)
⚫ Cones comprise two spectral
types
⚫ Diurnals- dichromatic vision
with more cones blue UV
cones and green type
⚫ Dim red light – out of the
visible spectrum –
insensitive
360nm
560nm
530nm
650nm
590nm
570nm
510nm
445nm
22. VISION
⚫ Sodium lamps - yellow – orange (589 and 589.6 nm)
light - better (good visibility to human but rodents
behave as if dark)
⚫ Ultraviolet spectrum (100-400nm) visible for rodents
but not for human –urine - mark visibility, night vision
⚫ It is easy to train rats to behaviorally differentiate
brightnesses, but difficult to train them to behaviorally
differentiate colors (Jacobs et al. 2011).
⚫ Albino rat ?
Photograph of a cage shelf under normal light (left)and ultraviolet light (right).The
rats' urine marks, faintlyvisibleunder normal lighting conditions,glow under the
black light.
23. WHAT CAN RATS SEE ?
Normal human vision
Normally-pigmentedrats have blurry
dichromaticvision with low color
saturation
Albino rats may see a very blurry,
light-floodedworld
On a bright day, albino rats may be
completely dazzled
24. HEARING WITH WHISKERS
⚫ Whiskers organized in a grid with five horizontalrows and 5 to 9 columns
⚫ Whiskers resonate at certain frequencies, (strings of a harp),
⚫ Longer whiskers vibrate at lower frequencies; shorter whiskers at higher frequencies.
Sshort whiskers near the nose and long ones further back, array of whiskers creates an
orderly map of frequencies on face (Neimark et al. 2013).
⚫ Each whisker is wired to a specific locationin the brain's sensory cortex that matches
the layout of the whiskers on the face, and thus matches the resontant frequencies of
the whiskers. (Andermann et al. 2014).This layout - neural representation of the
auditorysystem.
⚫ Whisker vibrationshows the extreme sensitivityof the rat's sense of whisker-
touch. Rats can make fine distinctionsbetween differenttextures,
26. OLFACTION
⚫ 1% of rat’s genes code for olfaction
⚫ 500-1000olfactory receptors + vomeronasal organ
⚫ Rodents use a variety of specialized scent glands, togetherwith
urine, faeces and vaginalsecretions for olfactory communication
◦ Identification of pups
◦ Home cage: familiar vs. unfamiliar animals (differentiate
strangers from members of one's own colony)
◦ Social status (dominant from subordinate individuals)
◦ Reproductive status: if the urine is from a female, rats can
determine whether she is receptive to mating, pregnant, or lactating.
◦ Sexual maturity (juvenile vs. sexually mature adult)
◦ Individual recognition
◦ Stress level
⚫ Cleaning of cages?
28. HEARING
⚫ Reception of the low - frequency vibrations
transmitted via both the air and seismically through
the ground
◦ In labs - sources of low frequency air or seismic waves in the
laboratory (e.g. construction work, lifts, cages or racks being
moved or knocked, items being dropped) – AVOID
⚫ Provide opportunity to build tunnel systems for
them to communicate effectively
⚫ ULTRASOUND – Distress,play, coitus,etc.
environmental – metal cage, taps, computers
29. SOUNDSAND HEARING
⚫ Humans can hear sounds from about 16 to 20,000 Hz
(20 kHz)*. Anything above 20 kHz is called
"ultrasound," because those sounds are higher than
we can hear. Anything below 20 Hz is called
infrasound
30. SOUNDS AND HEARING IN RAT’S
WORLD
⚫ Rats can hear ultrasound: the range of the rat's
hearing is around 200 Hz to 80 or 90 kHz
⚫ There is a whole world of high frequency sound
around rats which rats can hear but we cannot, a
perceptual difference that humans tend to forget
For example, when a human gently rubs
thumb and forfinger together, we hear nothing. But
this movement makes a scratchy sound in the
ultrasonic range.
⚫ Wire cages make a lot of ultrasonic noise in addition
to audible noise when rats move around in them.
31. RATS AND ULTRASOUND
What ultrasounds can a rat make?
⚫ Rats emit long 20 kHz vocalizations when they are unhappy or stressed.
These calls are emitted when an adult or juvenile is defeated socially ,
sees a predator, experiences pain or anticipation of pain or when an
untame rat is handled
⚫ 30 to 50 kHz range: Infant rats produce very high pitched distress calls.
These cries elicit maternal care such as retrieving the infants to the nest
⚫ Rats also emit short, high-pitched calls under positive contexts. Adults
and juveniles emit them during rough and tumble play and in
anticipation of feeding
⚫ Male and female rats also call in a sexual context . Before copulation,
males and females emit calls as they approach and sniff each other.
Female calling also solicits male sexual behavior.
32. FUNDAMENTALS
⚫Reproductivelife span:8 months
⚫Fertility:2- 5 litters(straindependent)
⚫Gestation:19-21 days (straindependent)
⚫Littersize:strainspecific (2-12pups)
⚫Weaning age:21 days (28 days) based on weight
⚫Estrous length :4 -5 days
⚫Hemochorialdiscoid placentation
33.
34. BREEDING – ESSENTIALS
⚫ Estrous cycle
⚫ Pheromone effect
⚫ Vaginal plug detection
⚫ Pregnancy determination
⚫ Age and sex determination
⚫ Mating systems
⚫ LitterFostering
⚫ Enrichment
⚫ Identification and breeding
record
35. Mice
⚫ 4 days of cycle
⚫ Metestrus (22
hrs)
⚫ Diestrus (33 hrs)
⚫ Proestrous (21
hrs)
⚫ Estrus (21 hrs)
Rat
🠶 4 days ofcycle
🠶 Metestrus (22 hrs)
🠶 Diestrus (57 hrs)
🠶 Proestrous (12 hrs)
🠶 Estrus (12 hrs)
STAGES OF OESTRUS CYCLE
36.
37. MATING SYSTEMS
⚫ Pair mating: 1 male – female : long term (post-
partum estrus)
⚫ Trio mating: 1 male – 2 females (remove pregnant
female from cage)
⚫ Harem mating: 1 male – up to 4 females
⚫ Timed (hand) mating: to know exact time of
mating and parturition (female placed with
male for a short time)
38. CHECKING FOR PLUGS
Checking females
for plugs is best
done in the early
morning (before
9:00 a.m.) if the
animals are
housed under a
typical 12/12 light
cycle.
38
39. MATING CONFIRMATION
⚫ Vaginal plug
◦ Plug detection = 1st day of pregnancy
◦ – However, plug ≠ pregnant &
◦ – No plug ≠ not pregnant
⚫ Sperm presence in vaginal smear
44. LITTER FOSTERING
⚫ The foster mother must have a healthy and well-fed litterof
her own that is withinone or two days of age of the
fostered pups
⚫ Pups different color than that of the fosterlings– better
⚫ The foster littershould be no larger than the natural litter
⚫ Litter is larger than six pups - divide
⚫ Remove the proposed foster mother and place her in a
holding pen
⚫ Place the fosterlingsin the foster mother’s home pen and
cover them with some nest material or bedding so they
acquire her scent and the scent of her pups.
⚫ Alternately, putting a heavy perfume scent on her nose before
introducingher to the fosterlingsmay mask theirscent
⚫ Check for milk spot
⚫ May be required in
◦ lethal milk (Slc30a4lm)
45. PRODUCTION DATA
⚫Littersize:Avg.no. of pups born
⚫Wean rate:Avg.no. of pups weaned
⚫Litterinterval:Avg.time between litter
⚫Weaning interval:Avg.time between
weaning litters
⚫Production index: Avg.no. of pups/
reproductive life of females
⚫Sex ratio: Weaned male: weaned female
47. ⚫Superfetation is simultaneous
occurrence of more than one stageof
developing offspring in the same
animal.
⚫Manifests as the formation of an embryo
from a different estrous cycle while
another embryo or fetus is already
present in the uterus.
⚫Superfecundation: When two
separate instances of fertilisation
occur during the same menstrual
cycle,
48. Lee–Boot effect
The Lee–Boot effect is a phenomenon concerning the
suppression or prolongation of oestrous cycles of mature
female mice (and other rodents), when femalesare
housed in groups and isolated from males
Whitten effect
occurs when male pheromones stimulate synchronous
estrus in a female population.
49. Bruce effect/ pregnancy block
is the tendency for female rodents to terminate their
pregnancies following exposure to the scent of an unfamiliar
male.
Vandenbergh effect
is aphenomenon in which an early induction of the first
oestrus cycle in prepubertal female mice occurs as a result
of exposure to the pheromone laden urine of a sexually
mature (dominant) male mouse
50. FACTORS AFFECTING BREEDING
PERFORMANCE
⚫ Birth defects in the pups. C57BL/6J (000664) -
hydrocephaly.,cleft palates,
⚫ Hybrid vigor. Hybrid mice tend to have more, larger,
and healthier litters
⚫ Strain-specific behaviors.The aggressive behaviors -
poor mothering instincts of others affect breeding
performance and pup survival.
◦ SJL/J (000686) males are aggressive and attack their
mates and offspring
◦ NZB/BlNJ (000684) females are poor mothers
◦ C57BL/6J (000664) females frequently lose their
first litter
51. FACTORSAFFECTING BREEDING
PERFORMANCE
⚫ Mutations and transgene effects. Some induced mutations are
embryonic lethal; some cause infertility or reduced fertility; some
affect mammary gland function
◦ C57BL/6J-Slc30a4lm/J(lethal milk mutation) produce milk that is
lethal to mice nursed due to a deficiency of zinc in the milk.
⚫ Light intensityand light cycle. Because mice generally breed at
night, breeding performance is best when a consistent and
uninterrupted light-dark cycle is maintained
◦ We use a 14-hour lights on/10-hour lights off cycle. Wild-derived
inbred mice breed better in relatively darker conditions than do
other strains.
⚫ Noise and vibrations. decrease breeding performance and may
induce the mothers to cannibalize their pups Construction-
related noises and vibration
52. FACTORS AFFECTING BREEDING
PERFORMANCE
◦ Barometricpressure:Falling barometric pressure can make some
strains hyperactive and decrease their breeding performance
◦ DBA/2J, (000671)
◦ Temperature and humidity : Laboratory mice breed best when the
temperature is between 16-26oC and the humidity is between 40-
60%.
⚫ Odours. Noxious fumes, perfumes, and other strong odours can
decrease breeding performance
⚫ Nutrition.Nutrition affects breeding performance
◦ BALB/cJ (000651) mice breed better when fed a diet containing
11% fat
◦ DBA/2J (000671) mice breed better when fed a diet containing
4% fat
53. FACTORS AFFECTING BREEDING
PERFORMANCE
⚫Feed placement.Obese mice may not
reach hopper, so provide feed inside the
cage
⚫Handling. mice with new litters should be
handled as little as possible
⚫Stress factors. Environmental changes
⚫Strain effect. inbreeding depression
54. IDENTIFICATION AND RECORD
KEEPING
⚫ Identification:
◦ Tattooing, metal clip, ear notching
⚫ Record keeping:
Mating unit system Litter system
Strain Litter ID
Assigned # of parent DOB
DOB No. of pups
Litter number Assigned no of cage
born
Date of mating
55. TIPS…
⚫ Minimize noise and traffic
⚫ Allow male mice in the cage from some time before female
⚫ Rotate female
⚫ “Do not disturb”
⚫ Don’t bang cages
⚫ Retire female and male at 8 months
